1. Field of the Invention
The present invention relates to a device for measuring and dispensing volumes of a liquid such as viscous solutions, suspension, or low density organic solutions accurately, reproducibly and quickly. More specifically, the present invention relates to a double-plunger syringe-type device which measures and dispenses liquid volumes without having air space between the plunger and the liquid.
2. Prior Art
Often in liquid volume measuring and dispensing for analytical sampling, a volume greater than one milliliter is required for accurate samplings (e.g. 5.0 ml or 10.0 ml). All of the prior art of positive displacement syringe pipets deliver less than one milliliter of liquid volume, with the exception of the pipet in U.S. Pat. No. 4,023,716, which dispenses a maximum volume of one ml of liquid. The pipet in the U.S. Pat. No. 4,023,716, however, suffers due to the large contacting surface of the syringe plunger with the inner surface of the syringe barrel and tip; it fails to deliver a liquid completely and accurately. Also, the syringe barrel is snapped weakly onto the main body of the device, and so it is easily snapped off from the body of the device during the delivery of a liquid sample in the barrel. The accuracy also varies due to the shifting positions of the adjustable plunger shaft; accordingly, frequent adjustment is required. U.S. Pat. No. 4,672,657 (McDermott) does not use a double-plunger liquid displacement system and it is only for the purpose of measuring micro volumes of liquid. U.S. Pat. No. 4,036,064 (Hydo) uses a system for mixing a reagent and a sample in a syringe barrel by a three-step operation and the inner plunger does not reach the end of the syringe tip for a complete delivery of a solution. U.S. Pat. No. 4,333,458 (Margulier) describes a system for a direct injection of an injectable solution from a glass cartridge ampule by a large plunger which holds the cartridge and a small rod which has an arrow tip engaging to the rubber plug of the cartridge ampule. These plungers do not contact with the solution. No current device is known to measure and dispense liquid volumes with a double-plunger syringe-type pipet, or with a firm and secure syringe barrel mounting mechanism (such as a bayonet mounting mechanism).